The present invention relates to an internal combustion engine for motor vehicles and the like.
As is known, internal combustion engines are currently being tested in which the intake and exhaust valves that selectively bring the combustion chamber of the engine into communication with the intake manifold and the exhaust manifold respectively of the engine are actuated by electromagnetic actuators driven by an electronic control unit. This solution makes it possible to vary the opening and closing moments of the valves in a very precise manner as a function of the angular speed of the crankshaft and of other operating parameters of the engine, substantially increasing the performance of the engine.
The electromagnetic actuator that currently provides the best performance is disposed alongside the stem of the valve of the internal combustion engine to be axially moved and comprises a support frame secured to the head of the internal combustion engine, an oscillating arm of ferromagnetic material having a first end hinged on the support frame in order to be able to oscillate about an axis of rotation perpendicular to the longitudinal axis of the valve, and a second end shaped as a curved finger disposed in abutment on the upper end of the stem of the valve, and a pair of electromagnets disposed on opposite sides of the central portion of the oscillating arm in order to be able to attract, on command and alternatively, the oscillating arm by causing it to rotate about its axis of rotation.
The electromagnetic actuator lastly comprises two elastic members, the first of which is adapted to maintain the valve of the engine in a closed position and the second of which is adapted to maintain the oscillating arm in a position such as to maintain this valve in the position of maximum opening. The two elastic members act in opposition against one another and are dimensioned such as to position, when both electromagnets are deactivated, i.e. in a condition of equilibrium, the oscillating arm in a rest position in which it is substantially equidistant from the polar heads of the two electromagnets so as to maintain the engine valve in an intermediate position between the closed position and the position of maximum opening.
Unfortunately, the electromagnetic actuators described above operate well, i.e. are able to ensure the full opening and closing of the intake and exhaust valves of the engine, only when the engine is operating at a relatively low speed of rotation. Experimental tests have shown a substantial deterioration of the engine performance at speeds of rotation higher than 6000 rpm that can be directly attributed to the malfunction of the electromagnetic actuators. This structural drawback is obviously incompatible with the maximum speeds of rotation achieved by internal combustion engines of small and medium cubic capacity that are currently commercially available.
In order to remedy the drawbacks described above, tests have recently started on internal combustion engines in which the intake and exhaust valves of the engine are moved by means of electro-hydraulic actuations which are obviously also driven by an electronic control unit.
Tests are in particular being conducted on internal combustion engines which comprise, for each intake or exhaust valve of the engine, a linear hydraulic actuator adapted axially to displace the corresponding valve from the closed position to the position of maximum opening by overcoming the action of an elastic member adapted to maintain this valve in the closed position, and an electrically controlled hydraulic distributor adapted to regulate the flow of pressurised oil to and from the hydraulic actuator so as to cause the valve to be displaced between the closed position and the position of maximum opening.
In order to meet the demand for pressurised oil, the internal combustion engines being tested are further provided with a hydraulic circuit which comprises an oil collection tank in which the oil to be supplied to the actuators is stored at ambient pressure and a pumping unit adapted to supply pressurised oil to the various hydraulic distributors by taking it directly from the collection tank.
Each electrically controlled hydraulic distributor is connected to the hydraulic circuit so that it can bring the corresponding linear hydraulic actuator into direct communication respectively with the delivery outlet of the pumping unit when it is necessary to displace the valve from the closed position to the open position, and with the collection tank when it is necessary to displace the valve from the open position to the closed position. In the former case, the pressurised oil is caused to flow into the linear hydraulic actuator. In the latter case, the pressurised oil filling the linear hydraulic actuator is caused to flow directly into the collection tank.
In other words, therefore, all the pressurised oil supplied to the hydraulic actuator during the displacement of the valve from the closed position to the position of maximum opening, is discharged directly into the collection tank during the displacement of the valve from the position of maximum opening to the closed position under the action of the elastic member adapted to maintain this valve in the closed position.
The main drawback of the solution using electro-hydraulic actuators described above is that the pressurised oil demand is particularly high and, moreover, increases proportionally with the number of revolutions of the engine and requires the use of pumping units that are so bulky that they are in practice incompatible with applications in the motor vehicle field.
The object of the present invention is to provide an internal combustion engine in which the electro-hydraulic actuators have a pressurised oil demand that is substantially lower than current actuators.
The present invention therefore relates to an internal combustion engine for motor vehicles and the like which comprises at least one intake and/or exhaust valve moving axially between a closed position and a position of maximum opening and means for moving the valves adapted to move, on command, at least this one valve between the closed position and the position of maximum opening, the valve movement means comprising an elastic member adapted to maintain at least this one valve in the closed position, a hydraulic actuator selectively adapted to move at least this one valve from the closed position to the position of maximum opening by countering the action of the elastic member, and a hydraulic circuit adapted to supply pressurised fluid to the hydraulic actuator, the hydraulic circuit comprising a delivery duct connected to the hydraulic actuator and pumping means adapted to supply pressurised fluid into the delivery duct, the internal combustion engine being characterised in that the pumping means comprise the elastic member and the hydraulic actuator.